1. Field of the Invention
The invention relates in general to a driving circuit, and more particularly to a multi-lamp driving circuit which generates equal current in each lamp of the backlight module.
2. Description of the Related Art
Referring to FIG. 1, a schematic diagram of a conventional multi-lamp driving circuit is shown. A conventional multi-lamp driving circuit 10 includes at least a main transformer 110, a balance transformer 120, and lamps L(1) and L(2). The main transformer 110 has a secondary coil coupled to one end of the lamp L(1) and one end of the lamp L(2). Each of the lamps L(1) and L(2) has the other end coupled to the balance transformer 120. The balance transformer 120 has the same winding number in the primary and secondary coils, which are opposite in polarity.
When current of the lamps L(1) and L(2) is different, the primary and secondary coils of the balance transformer can respectively induce voltages of opposite polarity. Owing that the induced voltages have the same amount and opposite polarity, the current of the lamps L(1) and L(2) is approximately the same.
However, due to overlarge volume of the balance transformer, the available area of the printed circuit board (PCB) is reduced and the difficulty of circuit layout is increased. Besides, due to high cost of the balance transformer and requirement of one balance transformer for per two lamps, the production cost for a lamp driving circuit is increased along with the number of lamps.